Release agent for rolls and method for improving release properties of rolls

ABSTRACT

A release agent for rolls, particularly rolls in paper making such as press rolls is described which comprises one or more release active components and optionally conventional additives and which is in the form of a microemulsion. Suitable compositions include those which are essentially free from water and to which water is only added before actual application. The microemulsion or the microemulsion, which upon water dilution is at least intermediately formed, is unstable upon dilution with water to the application concentration which results in a good and homogeneous application of the active ingredients to the press surface. In this way the efficiency of the release agent and the release properties of the rolls are improved. Further, less deposits are formed on the roll surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of, and claims priority of PCTApplication Number PCT/US96/16345 filed Oct. 15, 1996 which claimspriority of German Application Number DE 195 39 523.9 file Oct. 24,1995.

BACKGROUND OF THE INVENTION

The invention relates to a release agent for rolls and to a method forimproving the release properties of rolls. In particular, the inventionis directed to a release agent for rolls like press rolls in papermaking and a method for improving the release properties of such rolls.

In many technical processes, continuous materials like films, webs etc.are passed over rolls. Depending on the conditions (temperature,pressure, moisture content etc.), the continuous material more or lessadheres to the roll so that a certain release force is required toremove the continuous materials from the roll. Therefore, such rolls areoften treated with release agents to lower said release force and tofacilitate removal of the continuous material from the roll. Thecomposition of such release agents differs widely depending on thenature of the continuous material passed over the roll, the material andthe surface state of the roll and the processing conditions. Generallyspeaking, such agents include release active agents, often also calledlubricants. Usually such agents are used pure or in form of an emulsion.

A problem often involved in the passing of a continuous material overrolls is that deposits are formed on the surface of the rollsoriginating from the ingredients or contaminants of the continuousmaterial. Such deposits adversely affect the performance of the rollsand eventually result in stopping the process so that the rolls can becleaned. To avoid such cleaning or to at least increase the intervals ofsuch cleaning interruptions, deposit preventing agents are used, thecomposition of which depends on the specific process, but mostlyincludes a polymeric substance.

Since known release agents and deposit preventing agents are often notfully satisfactory, it is an object of the present invention to providean improved release agent for rolls and a method using said agent forimproving the release properties of rolls. It is a further object of theinvention to improve the efficiency of substances used for preventingdeposits on rolls.

Thus, the invention relates to a composition in form of a microemulsionwhich comprises one or more release active components and upon dilutionwith water is useful as a release agent for press rolls in papermakingsystems, which is characterized in that it breaks upon dilution withwater.

Further, the invention relates to a composition which comprises one ormore release active components, forms a microemulsion upon addition ofan appropriate amount of water, and upon further dilution with water isuseful as a release agent for press rolls in papermaking systems, whichis characterized in that the microemulsion breaks upon dilution withwater.

Furthermore, the invention relates to a method for improving the releaseproperties of rolls like press rolls in papermaking, which ischaracterized by diluting a microemulsion according to the inventionwith water to break the microemulsion and applying the dilutedmicroamulsion to the roll.

Preferred embodiments and advantages of the invention will becomeapparent from the following detailed description of the invention andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the effect of diluting various release agents on thesheet release force as measured in accordance with the test proceduredescribed in Example 1.

FIG. 2 illustrates the minimum, maximum and average sheet width of paperremoved from a press roll when using various release agents inaccordance with the test procedure described in Example 3.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is generally applicable to all kinds of rolls overwhich a continuous material is passed, the invention is particularlysuitable in paper mills and accordingly will be described in thefollowing with particular reference to papermaking and the specificproblems involved therein.

Known release active or lubricating agents, which are also useful in thepresent invention, for rolls in papermaking, particularly press rolls,are oils, water insoluble surfactants, water insoluble polymers andwaxes which are applied to the rolls (e.g., by spraying). While some ofthese release active substances can be applied pure, they are mostlyused in the form of an emulsion (macroemulsion) for ease of applicationand better distribution on the roll surface in combination with smalleramounts of active substance required in comparison to the use of thepure substance. However, it is known that these agents suffer from majororganic deposit problems and that they are unable to prevent organicdeposits.

It is now surprisingly found that the above problems can be overcome orat least considerably reduced if the release agent is in the form of amicroemulsion which is diluted with water prior to the application tothe rolls. Microemulsions are transparent dispersions containingparticles of less than 100 nm in size and mostly include an oilycomponent, a surfactant, a cosurfactant and water. Sometimes the oilycomponent and the cosurfactant can be the same. Usually microemulsionsare of low viscosity. The individual components are present in suchquantities that at least at room temperature stable, liquid,single-phase systems are formed. Suitable components for and thepreparation of microemulsions as well as the properties ofmicroemulsions are known and extensively described in the literature(see e.g., "Encyclopedia of Emulsion Technology", 1983 by Marcel Dekker,Inc.; "Milton J. Rosen, Surfactants and Interfacial Phenomena", SecondEdition, 1989, by John Wiley & Sons, Inc.; and M. Bourrel and R. S.Schlechter, "Microemulsions and Related Systems--Formulation, Solvencyand Physical Properties", Surfactant Science Series, Vol. 30, 1988,Marcel Dekker, Inc.).

Without being bound to a theory, it is believed that the improvementrelating to the present invention is based on the fact that whendiluting known release agents in the form of a macroemulsion, theemulsion droplets containing the release active ingredients are notphysically changed, while in contrast microemulsions are only stablewhen undiluted, and upon dilution become turbid, i.e., the releaseactive ingredients are set free from the solution. In other words,diluting a macroemulsion mainly increases the amount of continuous phasebut leaves the stability and thus the tendency of the emulsion dropletsto deposit on the roll surface relatively unaffected. In contrast, theparticles developing in microemulsions upon dilution have a much greatertendency to deposit on the roll surface. Accordingly, instability of themicroemulsion upon dilution is required to obtain the advantages of thepresent invention.

The present size of the active ingredients in microemulsions obtainedupon dilution is similar or preferentially larger than the particle sizeof corresponding macroemulsions. The larger the particles, the moredifficult it is to keep them stable, but the better become the releaseperformance. It would be very difficult to keep a macroemulsion stable(for six (6) months' shelf life) which has a particle size similar to amicroemulsion upon dilution. Accordingly, it would be necessary tosufficiently stabilize such macroemulsion by the addition of suitablestabilizers which in turn means that the oily component has a strongtendency to stay in the water phase. So it loses its functions again(see above). In contrast, microemulsions allow a stable six (6) months'shelf life and are triggered to be unstable only when the customer usesit, i.e., upon dilution. If the particle size of the dilutedmicroemulsion is too big (e.g., 150 μm or more), then the reducedsurface coverage is not counterbalancing the improved release anymoresince there are not enough particles to cover the surface of the roll(compare Example 4). Thus in general, it is preferred that themicroemulsion has a composition that the particles obtained upondilution have a size in the range of 10 to 150 μm, preferably 20 to 100μm (Coulter Counter, see Example 4).

It was further found that the release agents according to the presentinvention provide deposit prevention if water soluble polymers are addedwhich are well know for use as deposit inhibiting agents. Particularlysuitable are, for example, dicyandiamide-formaldehyde condensates. For amore comprehensive overview of suitable polymers reference is made to EP0 599 440 A1, the disclosure of which is herewith included by reference.

Besides the release active components and deposit preventing componentsthe release agents according to the present invention can includeconventional additives like acid, cleaning surfactants, salt etc.,provided they do not adversely affect the stability of the microemulsionand the efficiency of the release active and deposit preventingcomponents.

In the method for improving the release properties of rolls like pressrolls in papermaking the microemulsion release agents are diluted withwater to break the microemulsion and then the diluted microemulsion isapplied to the roll. In practice, the application concentration isusually in the 0.1 to 1.5% by weight and preferably the 0.2 to 1.0% byweight range,. i.e., the microemulsion is diluted with water to such adegree that the composition actually applied to the roll comprises 0.1to 1.5% by weight and preferably 0.2 to 1.0% by weight of the originalmicroemulsion.

According to an alternative embodiment of the present invention, it isalso possible to prepare a release agent which includes all thecomponents described above except for the water. The individualcomponents are present in such quantities that upon addition of water amicroemulsion is formed. In other words, this embodiment of the presentinvention relates to a kind of "concentrate or "potentialmicroemulsion", i.e., it is capable of forming a microemulsion upon theaddition of an appropriate amount of water. Since in practice a greatexcess of water is used (see above), in this embodiment of the inventionthe microemulsion state is just an intermediate one and themicroemulsion is broken immediately so that the release activeingredients are set free. Of course, the addition of water can bestepwise (two or more points of adding water when transporting therelease agent to the roll) so that the microemulsion is actually formedand exists for a limited period of time.

The following examples are provided to illustrate the present inventionin accordance with the principles of this invention, but are not to beconstrued as limiting the invention in any way except as indicated inthe appended claims. All parts and percentages are by weight unlessotherwise indicated.

EXAMPLE 1

The sheet release of release agents in form of a microemulsion, amacroemulsion, an aqueous solution containing a cationic polymer and anaqueous solution containing an anionic polymer was investigated bydetermining the required release force depending on the degree ofdilution. In this test, a freshly prepared wet handsheet is pressed onthe sample roll material until a 40% consistency (40% fiber and 60%water) sheet is obtained, which adheres to the surface of the sampleroll material. Then the force required to peel off the paper from thesample roll material is measured.

The results are shown in FIG. 1 in which a concentration of 100%designates the undiluted release agent while a concentration of 0.1%designates a composition comprising 99.9% by weight water and 0.1% byweight of the original undiluted release agent.

The macroemulsion consisted of 20% by weight of a modified animal oil,7.5% by weight of a mixture of two non-ionic surfactants and 72.5% byweight of water. The microemulsion consisted of 8.7% by weight of amodified animal oil, 11.1% by weight of cationic polymer, 13.7% byweight of 2-butoxyethanol, 17.2% by weight of non-ionic surfactant, 1.3%by weight of cationic surfactant and 48% by weight of water. The aqueoussolution of the cationic polymer consisted of 2.5% by weight of cationicpolymer, 5% by weight of non-ionic surfactant, 0.02% by weight ofphosphoric acid and 92.48% by weight of water. The aqueous solution ofthe anionic polymer consisted of 5% weight of anionic polymer, 10% byweight of a 50% aqueous solution of an anionic surfactant and 85% byweight of water.

It can be seen from FIG. 1 that the release performance isproportionally less by diluting a macroemulsion. By diluting amicroemulsion an increase in release performance of a 10% microemulsioncompared to the 100% version is observed. Its performance remainssubstantially constant while further diluting up to about 1%. Thus asmall amount of oil performs better in a microemulsion than a largeamount of the same oil formulated into a macroemulsion.

EXAMPLE 2

Laboratory and field release tests were performed to compare themicroemulsion according to the present invention with conventionalaqueous solution and macroemulsion type products. The laboratory releasetests were carried out as described in Example 1. in the field releasetests the products are applied on the press roll via a spray bar. Thepoint of release of the paper web from the roll is measured in cm. Theresults are shown in the following table.

    ______________________________________                                                                      Point of                                                                      Release (cm)                                                  Sheet Release Force(N/m)                                                                      Field Test                                      Tested Products                                                                             Field Test at 2000 ppm                                                                        at 8000 ppm                                     ______________________________________                                        Blank (water) 1.80 ± 0.10  0                                               Aqueous cationic I                                                                          1.73 ± 0.02  0.5                                             Aqueous cationic II                                                                         1.47 ± 0.02  0.4                                             Non-ionic macroemulsion                                                                     1.21 ± 0.04  0.8                                             Cationic microemulsion                                                                      1.08 ± 0.04  1.5                                             ______________________________________                                    

The aqueous cationic I solution was a commercial product and consistedof 20% by weight of cationic polymer, 5% by weight of non-ionicsurfactant, 5% by weight of phosphoric acid and 70% by weight of water.Aqueous cationic II was the same product as used in Example 1. Thenon-ionic macroemulsion consisted of 20% by weight of a modified animaloil, 7.5% by weight of a mixture of two non-ionic surfactants, 1% byweight of cationic surfactant, 2.23% by weight of phosphoric acid and69.27% by weight of water. The cationic microemulsion according to theinvention consisted of 8% by weight of a modified animal oil, 2% byweight of cationic polymer, 19% by weight of non-ionic surfactant, 19%by weight of 2-butoxyethanol and 52% by weight of water.

The best results show that the microemulsion according to the presentinvention results in the lowest release force. In agreement therewith,it provides the highest point of release.

EXAMPLE 3

In another field trial different microemulsions were tested and comparedto conventional aqueous solution and macroemulsion type products. Inthis test the sheet width of the paper web removed from the press rollwas determined. The sheet width decreases with increasing release forcerequired for removing the paper web from the roll. The broader thesheet, the smaller the release force required. The results of the fieldtrial are shown in FIG. 2.

Product 7306 was a commercial product which is an aqueous solution of acationic polymer and consists of 17.0% by weight of a first cationicpolymer, 2% by weight of a second cationic polymer, 0.5% by weight of acationic surfactant, 5% by weight of phosphoric acid and 75% by weightof water. Product 27-5 was a macroemulsion and consisted of 19.9% byweight of a modified animal oil, 2.49% by weight of a non-ionicsurfactant (ethoxylated castor oil, HLB 15), 4.98% by weight of anothernon-ionic surfactant (ethoxylated fatty acid, HLB 5), 1% by weight ofoleyl bis (2-hydroxyethyl)amine, 5.1% by weight of dialkyl(C₈-C₁₀)dimethyl ammonium chloride, 5.1% by weight of phosphoric acid (85%)and 66.03% by weight of water. Products 27.1 to 27.4 were microemulsionswith the following compositions.

27-1: 8% by weight of a modified animal oil, 2% by weight ofdicyandiamide-formaldehyde condensate (50% aqueous solution), 20% byweight of ethoxylated (3 EO) C₁₃ -fatty alcohol, 16.8% by weight oftriethylene glycol monobutyl ether, 2% by weight of dialkyl(C₈-C₁₀)dimethyl ammonium chloride, 0.04% by weight of phosphoric acid(85%) and 51.16% by weight of water.

27-2: 7% by weight of a modified animal oil, 2% by weight ofdicyandiamide-formaldehyde condensate, 20% by weight of ethoxylated (3EO) C₁₃ -fatty alcohol, 16.8% by weight of triethylene glycol monobutylether, 2% by weight of dialkyl(C8-C₁₀)dimethyl ammonium chloride, 0.04%by weight of phosphoric acid (85%), 1% by weight of isoparaffin and51.16% by weight of water.

27-3: 2.01% by weight of a modified animal oil, 1.99% by weight ofdicyandiamide-formaldehyde condensate, 19.92% by weight of ethoxylated(3 EO) C₁₃ -fatty alcohol, 13.94% by weight of triethylene glycolmonobutyl ether, 3.78% by weight of dialkyl (C₈ -C₁₀)dimethyl ammoniumchloride, 0.02% by weight of phosphoric acid (85%) and 60.34% by weightof water.

27-4: 8% by weight of a modified animal oil, 2% by weight of cationicpolymer, 19% by weight of 2-butoxyethanol, 19% by weight of ethoxylatedC₉ -C₁₁ -alcohol and 52% by weight of water.

The test results shown in FIG. 2 clearly demonstrate that themicroemulsions according to the present invention result in a lowercontraction of the paper sheet indicating easier removal from the rolldue to a lower release force.

EXAMPLE 4

As explained above, it is required that the microemulsion is unstableupon dilution with water for optimal performance. An unstable emulsionperforms better than a stable one. The oil droplets are then "ejected"from the water and absorb more strongly on the roll surface. Further,the microemulsion upon dilution has to provide enough particles to coverthe surface of the roll. However, the optimum composition for themicroemulsion can be easily determined by diluting it with water andmeasuring the particle size of the turbid composition obtained bydilution.

The test results, (see Example 1 for description of test conditions)summarized in the following table, were obtained by diluting themicroemulsions to a concentration of 0.2%, i.e., by adding 99.8% byweight of water. Particle size was determined using a Coulter Counter LS130. The maximum of the obtained particle size distribution (volumedistribution) is given as particle size.

    ______________________________________                                                      Release Force                                                   Microemulsion Containing                                                                    (Blank = 1.90 N/m)                                                                         Comment                                            ______________________________________                                        8% oil X/0% A 1.51         Clear upon dilution/                                                          no particles                                       8% oil X/1% A 1.11         Turbid upon dilution                               8% oil X/20% hydrophobic                                                                    0.88         Turbid upon dilution/                              surfactant/3% A            12 μm particle size                             6.7% oil X + 1.3% oil Y                                                                     0.82         Turbid upon dilution/                              20% hydrophobic            32 μm particle size                             surfactant/3% A                                                               4% oil X + 4% oil Y                                                                         0.84         Turbid upon dilution/                              20% hydrophobic            116 μm particle size                            surfactant/3% A                                                               8% oil Y      0.91         Turbid upon dilution/                              20% hydrophobic            153 μm particle size                            surfactant/3% A                                                               ______________________________________                                    

In the above table, oil X is a modified animal oil, oil Y is anisoparaffin oil, the hydrophobic surfactant is ethoxylated (3 EO) C₁₃-fatty alcohol, and A is dialkyl (C₈ -C₁₀)dimethyl ammonium chloride.

As can be seen from the results summarized in the above table, the firstmicroemulsion was too stable and thus did not free the oil particles.Accordingly, it remained clear upon dilution and resulted in acomparatively high release force. The third, fourth, fifth and sixthmicroemulsion only differ with regard to the composition of the oilcomponent. As can be seen, the lowest release force was measured for thefourth microemulsion providing a particle size of 32 μm.

We claim:
 1. A method for improving the release properties of rollscharacterized by the steps of (a) diluting a release agent which is inthe form of a microemulsion with water to break the microemulsion andform a composition wherein the composition comprises 98.5 to 99.9% byweight of water and (b) applying said composition to said rolls.
 2. Themethod as claimed in claim 1 wherein said diluted microemulsioncomprises 99.0 to 99.8% by weight of water.
 3. The method as claimed inclaim 1 wherein said release agent contains release active componentsselected from the group consisting of oils, water insoluble surfactants,water insoluble polymers, waxes, and mixtures thereof.
 4. The method asclaimed in claim 3 further comprising a deposit preventing component. 5.The method as claimed in claim 4 wherein said deposit preventingcomponent is a water-soluble polymer.
 6. The method as claimed in claim1 wherein said composition contains particles having a size from 10 to150 μm.
 7. The method as claimed in claim 1 wherein said rolls are pressrolls in papermaking systems.